"Getting past the pure joy of seeing these games run this fast, we
need to decide how valuable all of this scaling is to gamers in terms of
cost, etc. In all of my testing (with one exception) the benefits of
moving from single Radeon HD 5870 to a pair of cards in CrossFire
outweighed the move from two cards to three in terms of price/performance
results. In other words, the value of the second card was higher than the
third in terms of increasing the performance of the gaming system as a
whole. Take HAWX as an example: at 2560x1600 the 1->2 card scaling was
over 70% while the 2->3 card scaling was about 53%. While that is still a
nice bump in performance (in many cases seeing 50% scaling on any multi-GPU
configuration would be good news) obviously the third card follows the laws
of diminishing returns."